Cellulose products and method of making



Patented Feb. 15,1938

UNITED STATES PATENT OFFICE Samuel Isaac Hoddeson, New Brunswick, N. J.,and Roy Mackay Meikleiohn, New York, N. Y.,

assignors to General Chemical Company, New

'York, N. Y., a corporation of New York N Drawing. Application December5, 1935,

Serial'No. 53,002

11 Claims.

This invention relates in general to low viscosity cellulose productsand their manufacture.

It is particularly directed to a method of treating cellulose to preparean initial material which may be nitrated to yield directly lowviscosity nitrocellulose products.

The invention further-comprehends low viscosity cellulose as a newarticle of manufacture. The development of the nitrocellulose lacquer orvarnish industry has, in the past, been greatly impeded because of thehigh viscosity of solutions containing even a small proportion ofnitrated cellulose of the laquer or 12%i.50 nitrogen type. This hasretarded the general commercial application of such derivatives in theindustry since highly viscous products when dissolved or thinned to ausable consistency carry an insuflicient quantity of film-formingingre-' client to yield a film or coating of substantial thickness inone application. Hence numerous successive applications are required.

While the viscosity of cellulose has in the past been varied over a widerange, it has not been possible, as far as we are aware, to prepare acellulose of sufficiently low viscosity so that a nitrated cellulosesuitable for commercial use in lacquers or varnishes could be prepareddirectly therefrom. Accordingly it has been the practice to nitrate acellulose and thereafter to subject the nitrated cellulose to anaftertreatment for reducing its viscosity to within an appropriaterange. obtain nitrated cellulose products of sufllciently low viscosityfor commercial use in lacquers, paints, varnishes, etc. However, theaftertreatment of nitrated cellulose presents numerous objections.Chemical treatments result in reduced yields and produce a productdifilcult to bleach to a satisfactory color. Treatment in watersuspension under pressure presents a serious explosion hazard unlessequipment is designed to minimize this danger, and this involvesadditional expense for equipment and operation.

It will be evident, therefore, that a cellulose that may be nitrated toyield directly low viscosity products constitutes a substantial advancein the art.

It is knownthat celluloses such as cotton and 0 wood pulp may bepurified by treatment with alkaline liquors, and digestion in weaklyalkaline solutions is a customary step in the preparation of cotton fornitration. That such procedures could be manipulated to yield cellulosefrom which low viscosity second) products could,

In this manner it has been possible to be obtained directly uponnitration was not formerly known.

In accordance with the present invention, it has been discovered thatextremely low viscosity cellulose of high alphabeta-cellulose content 5(i. e. about 98% or more insoluble as determined by the usualsoda-soluble test for gamma cellulose) maybe obtained from ordinarycellulose such as cotton, or wood cellulose by employing a series oftreatments wherein the cellulose is 10 first treated with a dilutealkaline solution, then mercerized, and subsequently digested in weaklyalkaline solution. Furthermore, the low viscosity of the cellulose hasbeen found to inure to the benefit of nitrated cellulose preparedtherefrom 15 so that by utilizing nitration methods commonly employed anitrated cellulose (11%-12.8% nitrogen) of low viscosity is'obtainedwhich may be employed directly without further reduction in viscosityfor the preparation of nitrocellulose lacquers, varnishes, etc. of highconcentration.

The process of the present invention is especially applicable to cottonlinters, which constitute the usual raw material" for the preparation 0!nitrated cellulose. It is also applicable to treat- 25 ment of cellulosefrom other sources, cotton cellulose or alpha cellulose derived fromwood, bagasse, or other vegetable origin to yield products ofcorrespondingly reduced viscosity.

Cotton linters are purified by the preliminary 30 alkaline digestionwith the result that the subsequent mercerization liquid may efiectivelypenetrate the fibers, thus fats, oils, waxes, and any remnants of hullsare removed in the first step. The mercerization serves to effect animportant reduction of viscosity of the cellulose and at the same timeappears to render the cellulose molecule susceptible to furtherviscosity reduc tionby subsequent alkaline digestion. Sodium hydroxideor other alkali metal or alkaline earth compounds may be employed as thealkaline reagent. Thus KOH and the salts of sodium and potassium, suchas the carbonates, sulfides, sulfites, phosphates, and silicates may beemployed but the larger quantities required and/or the high prices ofmost of these reagents render their useless economical than the use ofcaustic soda.

The results will vary with conditions of treatment and in order tosecure the most satlsfactory products the initial material, such ascotton linters or refined wood pulp, may be digested for 3 to 15 hoursat a-temperature of 150 to 200 C. (under a pressure of to pounds persquare inch) in a-solution having a hydroxyl ion 55 concentrationequivalent to a solution containing .25% to 4.0% of NaOH. This serves toreduce the viscosity of the cellulose in terms of the viscosity ofnitrocellulose producible therefrom from as much as several thousand tobetween about 100 and about 1700. The treatment is preferably regulatedto yield a viscosity of 100 to 300 seconds. The treated cellulose isthen mercerized, for example by immersion in an aqueous solution havinga hydroxyl ion concentration equivalent to a solution containing 14% to28% NaOI-I maintained at 2 to 32 C. (35 to 90 E.) for a period of 3minutes to an hour. The mercerization preferably is regulated to furtherreduce the viscosity to between about 15 and about 60 seconds.

cellulose.

' The cellulose, after mercerization, is then again digested at atemperature of 150 to 200 C. (under a pressure of 60 to 150 pounds persquare inch)- for a period from 3 to 24 hours in an aqueous I solutionof to 3.0% NaOH or equivalent solution. This digestion serves to reducethe viscosity to that corresponding to second nitro- After'eachtreatment of the cellulose the excess 26 alkaline solution is drainedoff and preferably the cellulose is washed well with water andcentrituged prior to subsequent treatment.

The customary method of measuring the viscosity of cellulose comprisesdetermining the viscosity of a solution of 2.5 grams of the driedcellulose in 97 cc. of cuprammonium solvent (an aqueous solutioncontaining 3010.5 grams copper, 165 -2.0 grams NHa, and 10 grams ofsucrose per liter), referred to as /2 concentration".

85 As far as we are aware .no cellulose has been oflered to the tradeor. produced prior to the present invention which has a viscosity below3 seconds when dissolved in /2 concentration standard cuprammo'niumsolution. Acellulose exhibiting a viscosity of 3 seconds in asconcentration solution, upon nitration in the customany manner so as toobtain commercial yields,

- gives a nitrated cellulose of approximately 15 to 20 seconds viscosityin a 12.2% solution of standard a viscosity solvent, e. g.'the solventknown to the toluol) trade as 366 (20% ethyl acetate of 85-88% estercontent, 25% denatured alcohol 23,

Half second viscosity nitrocellulose has a viscosity in 20% solution(20%dry basis-nitrocellulose in standard solvent) of from 2 to 5seconds, equivalent to second in 12.2% solution. Viscositydeterminations :of products of half second viscosity are customarilymade in 20% solution for ease of manipulation.

cuprammonia is so much lower than the viscosity of-the 20% strength ofnitrocellulose that the as standard falling ball method can not beapplied to the cuprammonia solution. Neither can the celluloseconcentration be increased since the cuprammonia solution is not capableof dissolving any appreciable excess over the standard 5 grams ofcellulose.

In order, therefore, to establisha directrelae.; ti9nsliip between theviscosity of a cellulose and the nitfofillulowproduced therefrom, andpro-- vide a method of determining ,viscosity that can be applieddirectly to the cellulose, a di erent In view of the low viscosity ofthe cellulose Q Full strength ouprammonia Equivalent solution 20%conoontra- 12.2% oonnention nitrocollu: trot-ion nitrolose viscositycellulose Viscosity Viscosity viscosity. pipette method standard 1 ling#7 pipette ball method 2. 0 11. 0 2. 2 11. 4 2. 6 ll. 6 2. 8 11. 0 3. 412- 0 4. 2 12. 4 4. 4 l3. 0 5. 0 13. 0 5. 4 l3. 0 7. 8 15. 0 9. 2 14. 4l4. 6 16. 6 19. 8 17.2 44. 0 32 2 2. 0 124. 2 l8. 4 3. 2 161. 0 F3. 2 4.0 104. 0 65. 2 4. 8 3%. 0 10a 4 8. 0 m 0 I 1ft. 6 ll. 8

This tabulation covering 19 samples extends over the range of 2 secondsto 520' seconds for the 20% concentration 01 nitrocellulose and it willbe noted that for the direct preparation of A secon nitrocellulose(between 2 and 5 seconds in 20% concentration) a cellulose is requiredwhose full strength cuprammonia solution has a viscosity between 11 and13 seconds by the pipette discharge method. On the other hand, acellulose whose full strengthcuprammonia solution has a viscosity 01 2.6seconds by the standard falling ball method has a viscosity of 32.2seconds by the other words. requires nearly three times as long todischarge as does the cellulose suitable for direct preparation of 5'second" nitrocellulose.

pipette discharge method or, in

and the 20% solution of nitrocelhiloeedirectly prepared from this 2.6viscosity of 44.6 seconds. The following examples illustrate the processof the present inventidifsecond; has a Example 1.-1oo parts of rat dotteamen-s were mixed -with' 1100 parts of a 1% aqueous sodium hydroxidesolution and heated in a digester at a temperature of about 170 C.pounds per squareinch pressure) -for three hours. The treated cellulosewas then separated from the dilute caustic solution, washed.with water,and treated with 1500 parts of an aqueous 18% sodium hydroxide solutionmaintained at a temperature of about 18 to 14 C. (56 1 for 15 minutes.The mercerized cellulose was separated irom the mercerization. lye;washed with water. and heated with 1100 parts 01' aqueous 2% sodiumhydroxide solution for nine hours at a temperature of about C. Theproduct, which comprised more than 98% alpha-beta cellulose.

' was then washed thoroughly with water. The

washed cellulose product, when hitrated under .standard'conditions withthe usual nitrating 1 acid mixture yie1ded-'a (12%:.5% nitrogen)nitrocellulose product having'a viscosity of 4.2 w en tested n a 20%solution; 1. e. the

nitrated cellulose product was what is known as second nitrocellulose.

Example 2.100 parts of raw cotton linters were heated with 1100 parts ofaqueous .75% sodium hydroxide solution at 170 C. for 16 hours. Thetreated linters were then separated from the sodium hydroxide solution,washed with water, and mercerized for minutes in 1500 parts of anaqueous 18.25% sodium hydroxide solution maintained at around 12 to 14C. (53 to 57 F.). The treated cellulose was then separated from themercerization lye, washed with water, and digested for six hours in 1100parts of aqueous 2% sodium hydroxide solution at a temperature of 170 C.After this treatment the cotton linters were thoroughly washed withwater and nitratedin the customary manner. The nitrocellulose productpossessed a viscosity of 4.6 seconds in solution.

Emmple 3.100 parts of bleached sulfite wood pulp (about 85% alphacellulose) were mixed with 1100 parts aqueous 75% sodium hydroxidesolution and heated at a temperature of about 170 C. (100 pounds persquare inch pressure) for a period of five hours. The treated pulp wasthen separated from alkaline solution, washed with water, andtreatedwith 1500 parts of aqueous 18.6% sodium hydroxide solution for one hourat a temperature of about 22 C. (71 to 72 F.). The m'ercerized pulp waswashed with water to remove the concentrated caustic and was digestedwith 1100 parts aqueous 1.0% sodium hydroxide solution at a temperatureof 170 C. for a period of about 16 hours. This cellulose product, whennitrated in the usual manner, yielded a nitrated cellulose having aviscosity of 2.6 seconds in 20% solution.

Example 4.l00 parts of unbleached sulfite wood pulp were digested with1100 parts of an aqueous solution containing 0.5% sodium hy-' droxideand 0.5% sodium sulfite (NazSOaflHzO) at a temperature of about 170 C.for five hours. The product was separated from alkaline solution. washedwith water, and mercerized with 1500 parts of an aqueous 18.4% sodiumhydroxide solution for one hour at a temperature of about 22 C. (71 F).The mercerized pulp was washed with water and digested for 16 hours at atem- 1100 parts of an aqueous 1% sodium sulfite (NarSOaHHsQ) solution,the digested pulp was then separated from sodium sulfite solution andwashed with water. The washed pulp was mercerlzed with 1500 parts oi anaqueous 18.4% sodlmm hydroxide solution for one hour at a temperature of22 C. (71F). The mercerized pulp was washed with waterand digested for'16 hours in 1100 parts of aqueous 1% sodium hydroxide solution at atemperature of 170 C. The

product was then washed as in the preceding,

examples. The cellulose of this treatment. upon nitration, yielded anitrocellulose having aviscosity of 3 seconds in a 20% solution.

Ezamplefilrwo parts of wood pulp, refined by the soda process, weredigested for five hours at a nitrocellulose having a viscosity of 0.8second in 20% solution.

Example 7.-A kraft wood pulp was digested for five hours with 1100% ofits weight ofaqueous 0.75% sodium hydroxide solution at a temperatureabove 170 C. The digested pulp product was washed with water andmercerized in 1500 parts of 18.6% sodium hydroxide solution for a periodof one hour at a temperature of about 22 C. It was then washed withwater and redigested this time for a period of 16 hours in 1100 parts ofa 1% sodium hydroxide solution at a temperature of about 170 C. Thiscellulose, when nitrated under standard conditions and with a nitratingacid normally used in the nitratlngindustry, gave a nitrocellulosehaving a viscosity of two seconds in 20% solution.

The amounts of solutions employed in the three steps of the process arenot'critical but may be between 4 and 20 times the weight of thecellulose with highly satisfactory results.

The following example will serve to illustrate the usual nitrationprocesses by which low viscosity nitrocellulose products may be preparedfrom the cellulose'of the present invention. It is to be understood ofcourse that any of the well-known nitration methods yieldnitrocelluloses of similarly low viscosity.

Example 8.The processed cellulose is picked and dried to a moisturecontent not to exceed 1%. 100 parts of the dried cellulose are thennltrated with 5000 parts of mixed acid containing approximately 21% to22% HNOs, 60% to 61% H2804, and 17% to 19% H2O. The nitration is carriedout for 25 to minutes at a tempera ture of to C. The resultingnitrocellulose is then washed with water and stabilized by boiling in afinal aqueous wash having an acidity between .2% and .4% (calculated asH2804). The product represents 140 to 150 parts of nitrocellulose (drybasis), having a nitrogen content of from 11.7% to 12.1% and a viscosityin 20% solution of special solvent No. 366 within the 2 to 5 secondrange.

After stabilization the nitrocellulose is dewatered either in a filterpress or centrifuge and then dehydrated with ethyl alcohol or othersuitable dehydrating agent'in order to remove all water which isobjectionable in the preparation of lacquers, artificial leather, etc.it is then packaged in containers in an alcohol wet condi: tion, theproduct for storage and transportation containing approximately 30%alcohol and 70% nitrocellulose.

In the above examples proportions are ex 'fibers low viscositycellulose, which directly on nitration by the method herein describedyields a nitrocellulose of second viscosity, which comprises removingnon-cellulosic materials from the cellulose fibers, subjecting theresultant product to mercerization, and thereafter subjecting themercerized cellulose to the action of a dilute alkaline solution havingan alkalinity equal to at least of caustic alkali at a temperaturebetweenabout 150 C..and about 200 C. for between about 3 and about 24hours.

2. The method of preparing from cellulose fibers low viscositycellulose, which directly on nitration by the method herein describedyields a. nitrocellulose of ,5 second viscosity, which comprisestreating the cellulose fibers with a dilute alkaline solution,subjecting the resultant product to mercerization, and thereaftersubjecting the mercerlzed cellulose to the action of a dilute alkalinesolution having an alkalinity equal to at least /4% of caustic alkali ata temperature between about 150 C. and about 200 C. for between about 3and about 24 hours.

3. The method of preparing from cotton low viscosity cellulose, whichdirectly on nitration by the method herein described yields anitrocellulose of ,5 second viscosity, which comprises removing oils,waxes, fats, and hulls from the cotton cellulose, subjecting thecellulose to mercerization, and thereafter subjecting the mercerizedcellulose to the action of a dilute alkaline solution having analkalinity equal to at least 14% of caustic alkali at a temperature ofabout 170 C. for between about 3 and about 24 hours.

4. The method of preparing low viscosity cellulose, which directly onnitration by the method herein described yields a nitrocellulose of 39secohd viscosity, which comprises treating cellulose with an alkalinesolution corresponding to an aqueous solution containing between about34% and about 4% NaOH at a temperature between about 150 C. and about200 C. for between about 3 and about 15 hours, mercerizing the prodact,and treating the mercerized product with an alkaline solutioncorresponding to an aqueous solution containing between about and about3% NaOH at a temperature between about 150 and about 200 C. for betweenabout 3 and about so 24 hours.

5. The method of preparing from cotton, which has been freed from oils,waxes, fats, and hulls,

- low viscosity cellulose, which directly on nitration by the methodherein described yields a nitrocellulose of ,5 second viscosity, whichmethod comprises treating cotton thus' purified with an aqueous solutioncontaining between about 14% and about 28% sodium hydroxide at atemperature between about 2 and about 32 C. for between about 3 andabout 60 minutes, and heating the resultant cellulose product with anaqueous solution containing between about V and about 3% sodiumhydroxide at a temperature or about 170 C. for between about 3 and about24 hours.

B. The method of preparing low viscosity cellulose, which directly onnitration by the method herein described yields a nitrocellulose of v,sec ond. viscosity, which comprises treating cellulose with an aqueoussolution containing between about and about 4% of sodium hydroxide at atemperature between abouti50 and about 200 C. for between about 3 andabout 15 hours, treating theproduct with an aqueous solution containingbetween about 1.4% and about 28% sodium hydroxide at a temperaturebetween about 2 and about 32 C. for between about 3 and about 60minutes, and heating the resultant cellulose product with an aqueoussolution containing between about 14% and about 3% sodium hydroxide ata. temperature of about 170 C. for

between about 3 and about 24 hours.

7. The method of preparing from raw cotton linters low viscositycellulose, which directly on nitration by the method herein describedyields a nitrocellulose of ,5 second viscosity, which comprises treatingthe cotton linters with an aqueous solution containing between about andabout 4% of sodium hydroxide at a temperature between about and about200 C. for between about 3 and about 15 hours, treating the product withan aqueous solution containing between about 14% and about 28% sodiumhydroxide at a temperature between about 2 and about 32 C. for betweenabout 3 and about 60 minutes, and heating the resultant celluloseproduct with an aqueous solution containing between about and about 3%sodium hydroxide at a temperature of about C. for between about 3 andabout 24 hours.

8. The method of preparing from cellulose fibers low viscositynitrocellulose of the ,5 second type, which comprises removingnon-celiulosic materials from the cellulose fibers, subjecting theresultant product to mercerization, thereafter subjecting the mercerizedcellulose to the action of a dilute alkaline solution having analkalinityequal to at least of caustic alkali at a temperature of about1'70 C. for between about 3 and about 24 hours, and nitrating the"resultant product.

9. The method of preparing from cellulose fibers low viscositynitrocellulose of the second type, which comprises treating thecellulose fibers with a dilute alkaline solution, subjecting theresultant product to mercerization, thereafter subjecting the mercerizedcellulose to the action of adilute alkaline solution having analkalinity equal to at least 54% of caustic alkali at ,a temperaturebetween about 150 andfabout 200 C. for between about 3 and about 24hours, and nitrating the resultant product.

10. The method of preparing from cotton low viscosity nitrocellulose ofthe 55 second type, which comprises removing oils, waxes, fats, a dhulls from the cotton cellulose, subjecting e cellulose to memorization,thereafter subjecting the mercerired cellulose to the action of a"dilute alkaline solution having an alkalinity equal to at least ofcaustic alkali at a temperature of, about 170 0. for between about 3 andabout 24 hours, and nitraflng the resultant product.

11. The method of preparing from raw cotton linters low viscositynitrocellulose of the ,5 second type, which comprises treating thecotton linters product with an aqueous solution containing bep tweenabout and about 3% sodium hydroxide at a temperature of about 170 C. forbetween about 3 and about 24 hours, and nitrating the resultant product.

SAMUEL ISAAC nonmssou. ROY- MACKAY swarm-roan.

